During the coming year we will investigate: (1) The pathogenesis of lesion formation in T lymphocyte-depleted, infected mice. (2) The physiocochemical and biological character of the lymphokine ESP. (3) The development of various immune reactivities against antigenic material from cercariae. (4) The development and nature of glomerular lesions in chronic low-grade infection. (5) Eosinophilopoesis in the bone marrow during primary schistosomiasis. (6) The nature of the interactions of eosinophils and schistosomal eggs.